Production and recovery of propylene oxide by plural distillation



H. R. NULL ETAL' 3,350,419 PRODUCTION AND RECOVERY OF' PROPYLENE OXIDE BY PLURAL DISTILLATION 2 Sheets-Sheet l @www ATTORNEY Oct. 3.1, 1967 Filed Feb. 12, 1964 ajll LO Z E I L5 gf Inn/EDITORSl m HAROLD R. NULL U 9) LEON E. BOWL- ROBERT C.. BINNING QL'MJ mw ATTORNEY United States Patent O 3,350,419 PRODUCTION AND RECOVERY OF PROPYLENE OXIDE BY PLURAL DISTILLATION Harold R. Null, Florissant, Leon E. Bowe, Glendale, and

Robert C. Binning, St. Louis, Mo., assignors to Monsanto Company, a corporation of Delaware Filed Feb. 12, 1964, Ser. No. 344,404 17 Claims. (Cl. 260-348.5)

acyl esters of polyhydroxyalkanes, polyhydroxycycloalkanes, polyglycols or mixtures thereof, and recovering said propylene oxide and other valuable propylene oxidation products by means of parallel and serial distillation separation zones including a plural asher let-down system operating on the reactor eluent.

The present invention relates to the production and recovery of commercially valuable chemicals. More particularly, the present invention relates to the production and recovery of propylene oxide, Still more particularly, the present invention relates to the non-catalytic direct oxidation of propylene, with molecular many other lessvaluable oxygenated products of the reaction.

Among prior art processes for the production of propylene oxides are the well-known chlorohydrin process,

is essentially a two-step process involving, first, chlorohydrinating propylene With hypochlorous acid to form propylene chlorohydrin and, hydrolysis of this intermediate with calcium hydroxide to form the desired propylene oxide. This procedure is disadvantageous because it is not a direct route to the preparation of the epoxide and, also, gives rise to purified propylene substrates.

Vapor phase processes involving, e.g., the catalytic oxidation of propylene to the corresponding oxide, are disadvantageous ifo-r several reasons. For example, these processes require large volume equipment and the processes.

Direct routes for the oxides have been descrlbed in the prior art. For exam- 3,350,419 Patented Oct. 31, 1.967

oxide. For example, various specific oxidation catalysts, catalyst-solvent or catalyst-promoter-solvent systems have been described (U.S. Patents 2,741,623, 2,837,424, 2,974,161, 2,985,668 and Ianother approach is th hibitors such as nitrobenzene (U.S. Patent 2,780,635); of saturated hydrocarbons (U.S. Patent 2,780,634); another method describes the use of neualkali metal and alkaline earth metal or salts of these metals (U.S. Patent another approach involves, the

hydroxides, 2,83 8,5 24) catalysts in tain olen oxides.

While the addition of various additives in sorne prior art processes may accomplish the purpose for which they were used, c g., neutralization of acid by addition of alkaline substances, the

bonates, alkaline earth oxides, mildly basic heavy metal hydroxides, ammonium hydrates and metal hydrates, salts of Weak acids, e.g., acetic acid and other carboxylates such as metal salts of tartaric, stearic, oleic and palmitic acids. However, the

hydroxides and carbonates,

resinous materials which cause gumming of apparatus components.

It is, therefore, an object of the present invention to provide a process for the production and recovery of propylene oxide which is free of numerous limitations recited in prior art processes.

An object of this invention is to provide a liquid phase non-catalytic direct oxidation of oleins with molecular oxygen to produce and recover propylene oxide and other valuable oxygenated products.

A further object of the present invention is the elimination of numerous apparatus components heretofore required in separation and relining trains for the recovery of propylene oxide and other oxygenated products produced in the direct oxidation of olens.

A further object of this invention is to provide a liquid phase process for the production of propylene oxide which is not dependent upon the presence or absence of any catalyst; nor is it dependent upon the presence of waterimmiscible solvents or upon solvents containing added bullets or acid neutralizers or other additives or secondary treatments with alkaline materials to remove acidic components; nor is it dependent upon the presence of saturated compounds, initiators or anticatalysts; further, it is not dependent upon critical pH levels of the reaction mixture or geometries.

These and other objects will become apparent as the description of the invention proceeds.

The invention will be more fully understood by reference to the accompanying drawings which constitute a part of the present invention.

In FIGURE 1 is shown a diagrammatic ilow sheet illustrating a preferred embod-iment of the invention.

FIGURE 2 is also a diagrammatic flow sheet illustrating another embodiment of the invention.

The present invention comprises the production of propylene oxide and other valuable oxygenated products by the direct oxidation of propylene with molecular oxygen in the liquid phase, and to a novel means of separating and recovering the formed propylene oxide.

The liquid phase in which the oxidation occurs comprises solvents which are essentially chemically indifferent, high boiling with respect to the volatile oxidation products and are oxidatively and thermally stable under the condition of the reaction described. Further, the solvents employed in the present invention are highly resistant to attack by free radicals which are generated in the oxidation process. Moreover, the solvents employed in the instant invention are effective in assuaging the deleterious effects of acidic components, especially formic acid and to a lesser degree acetic acid, which are formed in the oxidation of oleiins. This assuaging effect is achieved, in part, by a proton solvation of the acidic components by the solvent which results in an acid-leveling which, in turn, permits substantially complete retention of the propylene oxide formed in the oxidation.

Solvents primarily and preferably contemplated herein comprise fully esteritied polyacyl esters of polyhydroxyalkanes, polyhydroxycycloalkanes, polyglycols and mixtures thereof. Polyacyl esters contemplated herein contain, generally, from 1 to 18 carbon atoms in each acyl moiety and from 2 to 18 carbon atoms in each alkylene or cycloalkylene moiety. However, best results obtain when the acyl moiety contains from 1 to 6` carbon atoms and the alkylene and cycloalkylene moiety each contains from 2 to 6 carbon atoms. These esters may be readily prepared by methods known to the art. For example, in U.S. Patent 1,534,752 is described a method whereby glycols are reacted with carboxylic acids to produce the corresponding glycol ester. Acid anhydrides may be used in place of the acids.

Representative glycols include straight chain glycols, such as ethylene glycol, propylene glycol, butylene glycol, pentylene glycol, hexylene glycol, heptylene glycol, octylene glycol, nonylene glycol, decylene glycol, dodecylene glycol, pentadecylene glycol and octadecylene glycol. Branched-chain glycols such as the iso-, primary, secondary and tertiary isomers of the above straight chain glycols are likewise suitable, e.g., isobutylene glycol, primary, second, and tertiary amylene glycols, 2-methyl- 1,2-pentanediol, 2methyl-2,4pentanediol, 2-ethyl1,3- hexanediol, 2,3-dimethyl-2,S-butanediol, 2methyl-2,3 butanediol and 2,3-dimethyl-2,3-dodecanediol. Polyalkylene glycols (polyols) include diethylene glycol, dipropylene glycol, tripropylene glycol, tetrapropylene glycol and dihexylene glycol.

In addition to straight and branched-chain glycols, alicyclic glycols such as 1,2-cyclopentanediol, 1,2-cyclohexanediol, l-methyl-l,2-cyclohexanediol and the like may be used.

Other suitable hydroxy compounds include polyhydroxy alkanes, such as glycerol, erthritol and pentaerythritol and the like.

Representative carboxylic acids include fatty acids such as formic acid, acetic acid, propionic acid, butyric acid, valerie acid, caproic acid, caprylic acid, lauric acid, palmitic acid, stearic acid, naphthenic acids, such as cyclopentane carboxylic acid, cyclohexane carboxylic acid, and aromatic acids such as benzoic acid and the like.

Representative polyacyl esters include polyacyl esters of polyhydroxy alkanes, such as triacyl esters of glycerol, eg., glycerol triacetate; tctraacyl esters of erythritol and pentaerythritol, e.g., erythritol tetraacetate and pentaerythritol tetraacetate and the like, and polyacyl esters of polyalkylene glycols (polyglycols), such as diethylene glycol diacetate, dipropylene glycol diacetate, tetraethylene glycol diacetate and lthe like. These polyacyl ester solvents may be used individually or as mixtures, being compatible with each other. For example, a mixture of varying proportions of a diacyl ester of a hydroxyalkane, such as propylene glycol diacetate, and a polyacyl ester of a polyglycol, such as dipropylene glycol diacetate, may be used. Or, a mixture of a polyacyl ester of a polyglycol, such as dibutylene glycol dibutyrate, and a polyacyl ester of a polyhydroxy alkane, such as glycerol trivalerate, or pentaerythritol tetrapropionate may be used as the solvent in the instant process illustrated in the example below.

Of particular interest in the present process are the vicinal diacyl esters of alkylene glycols, such as the diformates, diacetates, dipropionates, dibutyrates, divalerates, dicaproates, dicaprylates, dilaurates, dipalmitates and distearates, and mixtures thereof, of the alkylene and polyalkylene glycols recited above. Still more particularly, of great interest are the diacetates of ethylene and propylene glycols used individually or in admixtures of any proportion.

Polyacyl esters having mixed acyl groups are likewise suitable, e.g., ethylene glycol formate butyrate, propylene glycol acetate propionate, propylene glycol acetate propionate, butylene glycol acetate caproate, diethylene glycol acetate butyrate, dipropylene glycol propionate caproate, tetraethylene glycol butyrate caprylate, erthritol diacetate dipropionate, pentaerythritol dibutyrate divalerate, glycerol dipropionate butyrate and cyclohexanediol acetate valerate.

The above-recited polyacyl esters are more fully described and claimed as solvents in the direct oxidation of olens with molecular oxygen in copending U.S. application Ser. No. 259,388, filed Feb. 18, 1963, now U.S. Patent No. 3,153,058, which is a continuation-in-part of U.S. application Ser. No. 175,315, filed Feb. 23, 1962, now abandoned.

Monoacyl esters of polyhydroxyalkanes and polyglycols are unsuitable for use as a reaction medium according to the present process. The same is true of other hydroxy or hydroxylated compounds such as glycerin, glycols, polyglycols and hydroxy carboxylic acids. This is due to the present of an abundance of reactive hydroxyl groups which are susceptible to autooxidative attack, hence, introduce In the preferred mode of operation the polyacyl ester solvents used herein constitute the major proportion of the liquid reaction medium with respect to all other constituents including reactants, oxidation products and co- For example, a refinery grade hydrocarbon feedstock or a crude hydrocarbon feedstock containing, e.g., 50% by Weight of the olefin to be oxidized, e.g., propylene, and

by weight of saturated hydrocarbons, e.g., an alsuch as propane, may be used in quantities up to reactor may constitute as much as 75% by weight of the liquid reaction medium,

according to reaction conditions or recycle conditions.

When carrying out the invention according to the less present in the liquid reaction medium should be not less than 25% by weight of said medium in order to advantageously utilize the the like; ethers such as diaryl ethers, e.g., diphenyl ether; halogenated aryl ethers such as 4,4dichlorodiphenyl ether and the like; diaryl sulfoxides, e.g., diphenyl sulfoxide; dialkyl and diaryl sulfones, e.g., dimethyl sulfone and dixylyl sulfone and nitroalkanes, e.g., nitrohexane. While the foreaccruing from the use of these polyacyl esters can be utilized advantageously when substantially any relatively chemically indifferent diluent is combined therewith.

Therefore, the present invention in its broadest use c-omprehends the oxidation of olefin-containing feedstocks the reaction mixture in a liquid reaction medium consisting essentially of at least 25 by weight based on said medium of at least one fully esteried polyacyl ester described above.

In any case, the liquid reaction medium referred to herein is defined as that portion of the total reactor content which is in the liquid phase.

tion catalysts, promoters, polymerization inhibitors, etc., are required as in many prior art processes.

As noted above, no added catalysts are required in the present oxidation process. However, due to the versatility of the above-described solvents in the usual oxidation catalysts can be tolerated although period, no initiators or promoters are required, but may be used to shorten or eliminate the brief induction period, after which no additional initiator or promoter need be added.

Suitable initiators include organic peroxides, such as benzoyl peroxide, inorganic peroxides, such as hydroprocesses, enhances the separation and recovery of propylene oxides by the sequence of steps described in detail below.

In carrying out the or the olefin may be premixed with the solvent ably, up to 50% by weight based on the solvent and, preferably, from 5 to 30% by weight based on the solvent). Preferably, the olen is pre-mixed with the solvent and the oxygen-containing gas introduced into the ole- -solvent mixture incrementally, or continuously, or the (suitreducing the concentration of olefin in the liquid phase and reducing the rate of oxidation of the olefin, hence giving lower conversions per unit time.

Intimate contact of the reactants, olefin and molecular oxygen in the solvent is obtained by various means known to the art, e.g., by stirring, shaking, vibration, spraying, sparging or other vigorous agitation of the reaction mixture.

The olefin feed stocks contemplated herein include pure propylene, mixtures of propylene with other olefins, eg., ethylene, or olefin stocks containing as much as 50% or more of saturated compounds, e.g., propane. Olefinic feed materials include those formed by cracking hydrocarbon oils, paraffin wax or other petroleum fractions such as lubricating oil stocks, gas oils, kerosenes, naphthas and the like.

The reaction temperatures and pressures are subject only to those limits outside which substantial decomposition, polymerization and excessive side reactions occur in liquid phase oxidations of propylene with molecular oxygen. Generally, temperatures of the order of 50 C. to 300 C. are contemplated. Temperature levels sufficiently high to prevent substantial build-up of any hazardous peroxides which form are important from considerations of safe operation. Preferred temperatures are within the range of from 150 C. to 250 C. Still more preferred temperatures are within the range of from 170 C. to 210 C. Suitable pressures herein are within the range of from 0.5 to 350 atmospheres, i.e., subatrnospheric, atmospheric or superatmospheric pressures. However, the oxidation reaction is facilitated by use of higher temperatures and pressures, hence, the preferred pressure range is from to 200 atmospheres. Still more preferred pressures are within the range of from 50 to 100 atmospheres. Pressures and temperatures selected will, of course, be such as to maintain a liquid phase.

Propylene oxidation in the present process is auto- Icatalytic, proceeding very rapidly after a brief induction period. A typical oxidation of propylene in a batch run requires from about l to 20 minutes. Similar, or faster, reaction rates obtain in continuous operation.

The reaction vessel may consist of a wide variety of materials. For example, almost any kind of ceramic material, porcelain, glass, silica, various stainless steels, e.g. Hastelloy C, aluminum, silver and nickel are suitable. It should be noted that in the instant process where no added catalysts are necessary, no reliance is made upon the walls of the reactor to furnish catalytic activity. Hence, no regard is given to reactor geometry to furnish large-surface catalytic activity.

The oxidation products are removed from the reactor, preferably, as a combined liquid and gaseous mixture, or the liquid reaction mixture containing the oxidation products is removed to a products separation system, the most unique feature of which, in part, comprises a twoiiasher let-down arrangement. This arrangement in combination with the preceding propylene oxidation reaction and with succeeding product-separation steps constitutes a unique, safe, simple, economic and practical process for the commercial production and recovery of olefin oxides.

In regard to the two-fiasher let-down system, the principal advantages accruing from its use are that the twoasher system (1) utilizes the heat of the oxidation reaction in the initial separation of gaseous and liquid prodducts; this eliminates the need of cooling the reactor effiuent, (2) minimizes the amount of overhead solvent consistent with the maximum amount of olefin oxide, e.g., propylene oxide (P.O.); (3) minimizes the amount of total overhead solvent, resulting in a reduced solvent load on subsequent distillation columns. The advantages of this reduced solvent load are that smaller columns are required for the requisite products separations; (4) reduces the quantity of acidic components in solvent recycle streams, and (5) removes the bulk of `the xed gases and very volatile components, thus reducing the pressure requirements to `prevent excessive loss of product in subsequent processing steps. The total effect of these advantages is to provide an efficient, rapid, economical method for stabilizing the propylene oxide reaction mixtures while unloading solvent from the oxidation products and recycling solvent to the reactor. A single fiasher or distillation column cannot perform all these functions, while a plurality of distillation columns or stripping columns requires lon-g hold times, during which the propylene oxide is subject to decomposition, hydrolysis, polymerization or other side reactions.

Although more than two fiashers can be used, it is not economical to employ more than two.

A preferred specific embodiment of the present invention will be described with reference to FIGURE 1 in the accompanying drawing in connection with the direct oxidation of propylene lto lpropylene oxide in a continuous operation, and a specific novel method of separating and refining this valuable prod-uct from other oxygenated products formed in the reaction. Suitable variations in the propylene oxide separation train are also disclosed. Such conventional equipment as motors, pumps, valves, gauges, refi'ux condensers, reboilers, safety heads and the like are not shown in the drawing or referred to in the process description, but their inclusion is a variation readily apparent to those skilled in the art.

Example In this process a one-liter Magne Drive autoclave serves as the reactor portion of a continuous system. Solvent, propylene and oxygen are introduced through a bottom port directly below a Dispersimax turbine agitator operating at 1500 r.p.m. to obtain efficient mixing and internal `gas recycle. The reactor is heated electrically and temperature control is maintained by modulating water flow through internal cooling coils. Reaction temperatures are continuously recorded on a strip-chart.

In operation the reactants, 92% propylene and 95% oxygen, together with propylene .glycol diacetate, a preferred solvent, are pre-mixed and fed through line 10 to the base of reactor 11, operating at 750 p.s.i.g. and 200 C. The lmolar feed ratio of C3H6/O2 is 1.5. Total hold time is about 4 minutes. A variation is to provide two or more reactors in parallel operating under identical conditions and feeding the effiuent from these reactors into the flash system described below.

The reaction product, a combined gas-liquid efiiuent, is fed continuously to the first fiasher 13 of a two-stage iiasher let-down system. Flasher 13 operates at 150 p.s.i.a. pressure and 200 C. From this flasher rnost of the low and intermediate boiling components including all unreacted propylene, CO2 and at least one-half, and in this example approximately 65%, of the propylene oxide `goes overhead along with about one-third of the acids, e.g., formic and acetic acids, all dissolved gases and about 6-8% of solvent. Bottoms from flasher 13 are fed to the second flasher 18 operating at 30 p.s.i.a. and 200 C. Most of the residual propylene oxide, i.e., between 20% and 30% of that formed, about one-half of the remaining acids and 10-15% of the solvent are vaporizcd and taken overhead. Bottoms from fiasher 18 containing the bulk of the solvent, about `6% of the propylene oxide and about 30% of the acids, are fed through line 19 to absorber 20. A side stream 21 of the solvent effluent from fiasher 18 is fed to residue removal column 22 where residue, i.e., reaction products having boiling points above that of the solvent, is removed as bottoms and the solvent is removed overhead through line 23 and returned to the reactor via solvent recycle stream 44. Column 22 is heated to 190 C. at lthe top and 216 C. at the bottom at a pressure of 15 p.s.i.a. Sixteen plates and a reflux ratio of 0.75 are used in this column.

Overhead from fiashers 13 .and 18 are directed to condensers 15 and 14, respectively, operating with cooling water. Condenser is a partial condenser wherein uncondensables, including fixed gases, most of the CO2, about 6% of the total propylene -oxide and small amounts of propylene, i.e., about one-half of the unreacted propyene, 4and propane 'are separated from the condensables and fed through line 16 countercurrently Ito the solvent bottoms from flasher 18 to absorber 20. The absorber operates at 120 p.s.i.a. and approximately '70 C. at the top and 100 C. at the -bottom and has twelve plates.

Fixed gases O2, H2, N2, CH4, CO and CO2 are vented from the top of the absorber. Propane, propylene, propylene oxide -and other soluble components are absorbed in the solvent which is recycled to the reactor through line 44 or alternatively, further processed for propylene purification, yas will be discussed in connection with FIGURE 2.

Condenser 14 serves as a total condenser and the condensed liquids from this condenser are combined with those from condenser 15 and this combined stream containing 85-95% of the propylene oxide, about two-thirds of the acids and from 15-20% of the solvent is fed through line to distillation column 26. In this column propylene oxide and lower boiling components such as propylene, propane, acetaldehyde, methyl formate, and a small amount of residual CO2 are removed overhead, and water, acids, methanol, acetone, methyl acetate and residual solvent are removed to recover such commercially valuable by-products as acetic acid. Column 26 is heated to 40 C. at the top and 210 C. at the bottom and operates at 150 p.s.i.a. Forty plates are used with a reflux ratio of 0.16.

The overhead stream from column 26 is fed through line 27 to a C3 removal column 28. This column is heated C. at the top and 165 C. at the bottom and 300 p.s.i.a., and propylene, propane and any residual CO2 are removed overhead; propylene oxide, acetaldehyde and methyl formate are removed as bottoms. Thirty-four plates and a reflux ratio of 0.31 are used. The overhead from this column is fed through line 29 to a propanepropylene splitter column 30. This column is heated to 50 C. at the top and 55 C. at the bottom under 300 p.s.i.a. Ninety-four plates and a reflux ratio of 11.7 are utilized, Propane is removed from the bottom through line 34 and propylene is taken overhead through line 35 and recycled to the reactor. Some propane may be driven overhead, if desired, for recycle by increasing the temperature at the bottom of this column.

An alternative procedure for removing propane from recycle propylene is shown by the dotted lines in FIG- URE 2. The overhead from column 28 is fed through line 29 to combine with the overhead stream in line 16 from condenser 15 leading to absorber 20. As mentioned previously, the liquid bottoms from the absorber containing solvent, propylene and propane may be recycled directly to the reactor (as in FIG. 1) or further processed for propylene purification, i.e., propane removal. When the concentration of propane in the reactor tends to build up to a level which interferes with the propylene oxidation, additional, or excess, propane is prevented from being recycled to the reactor by directing the effluent from absorber 20, wholly or partially, through a sidestream line 45 taken from line 44, e.g., by means of a distributing valve (not shown) into desorber 46 operated at 50 C. at the top and 100 C. at the bottom and 300 p.s.i.a. pressure. Here, solvent is removed as bottoms and recycled to the reactor through line 44, and propane and propylene are removed overhead through line 47 to C3H6-C3H8 splitter column 30 operating at 300 p.s.i.a. and heated to 50 C. at the top and 55 C. at the bottom. Propane is removed as bottoms and propylene of essentially the same composition as the initial feed material is recycled through line 35 to the reactor propylene feed stream.

The bottoms from column 2S (FIGS. 1 and 2') conacetaldehyde and methyl formate is fed through line 31 to distillation column 32 for acetaldehyde removal. This column, heated to about 50 C. at the top and 60 C. at the bottom, operates at 33 p.s.i.a. pressure and utilizes 89 plates at a reux ratio of 39. Acetaldehyde is removed overhead through line 36.

Bottoms from methyl formate removal zone 38. In the present embodiment column 38 is an atmospheric (l5 p.s.i.a.) extractive distillation column having 54 plates and operating at about 50 C. at the top and 70 C. at the bottom. As entraining agent is used a hydrocarbon solvent boiling above 67 C. The upper boiling point of hydrocarbon solvents used in column 38 is limited only by practical engineering considerations. A preferred boiling point range for hydrocarbons used herein is from 67 C. to 250 C. In the present embodiment a Cfr-CB parainic naphtha fraction boiling between C. and 95 C. is used. Other hydrocarbon solvents which may alternaas solvent extraction, azeotropic and desorption, complex formatiom etc.

The entraining agent (weight solvent ratio=5) is fed to column 38 through line 39. Methyl formate is removed overhead through line 40 and a hydrocarbon-propylene oxide mixture is removed from the bottom through line 41 to distillation column 42. Column 42 is heated to about 50 C. at the top and about 1101 C. at the bottom under from the top.

In a typical run according to the present embodiment feed materials are added at approximately the following hourly rates: propylene, 530 g., oxygen, vent (propylene glycol diacetate), 4600 g. (reactor residence time about conversion is 54%, oxygen conversion is 99.9% and propylene oxide yield is about 46%.

While the invention has been specifically described with reference to the production and recovery of propylene oxide, it is within the purview of the invention to utilize the above-described and illustrated system for the oxidation of other olenic compounds to the corresponding olefin oxide and recovery thereof. It being understood that process conditions, e.g., temperatures and pressures in the reactor, ashers and columns will be modified accordingly to make the necessary separations.

Other olens suitable for use herein preferably include those of the ethylenic and cycloethylenic series up to 8 carbon atoms e.g., ethylene, propylene,

At steady state 4.0 minutes) propylene 8 carbon atoms. Included such as 2 methyl-1 butene, 2methyl2butene, Z-methyl-propene, 4-methyl-2-pentene, 2,3 dimethyl 2 butene and 2methyl2pentene. Other suitable olefinic compounds include dienes such as butadiene, isoprene, other pentadienes and hexadienes; cyclopentenes, cyclohexenes, cyclopentadiene, vinyl-substituted cycloalkyenes and benzenes, styrene, methylstyrene, and other vinyl-substituted aromatic systems.

It is to be understood that the foregoing detailed description is merely illustrative of the invention and that many variations will occur to those skilled in the art without departing from the spirit and scope of this invention.

We claim:

1. Process for the continuous production and recovery of propylene oxide which comprises the direct oxidation of propylene feedstocks with molecular oxygen in a solvent selected from the group consisting of fully esteritied polyacyl esters of polyhydroxyalkanes, polyhydroxycycloalkanes, polyglycols and mixtures thereof, wherein said esters contain from 1 to 18 carbon atoms in each acyl moiety and from 2 to 18 carbon atoms in each alkylene and cycloalkylene moiety, and recovering formed propylene oxide by:

(a) directing an eiuent stream of the reaction mixture from a reaction zone through a plurality of successive ashing distillation zones maintained at essentially the same temperature as the oxidation reaction, but each successive ashing zone being maintained at pressures substantially lower than in preceding ones and in said reaction zone in order to separate most of the low and intermediate boiling products as gas phase from the bulk of the solvent which is removed as bottoms from each flashing zone and directed to the succeeding one,

(b) passing said gas phase to condensing zones, from whence uncondensed gases are directed to an absorbing zone into which efuent solvent from said ashing zones is also passed to absorb uncondensed propylene and propylene oxide,

(c) directing a side-stream of said eiuent solvent in (b) through a polymeric residue having a boiling point above that of said solvent removal distillation zone where residue is removed as bottoms and solvent is distilled overhead and combined with the solvent bottoms from said absorbing zone and recycled to said reaction zone,

(d) passing a combined stream of condensed liquids from said condensing zones into an acids-separation distillation zone where organic acids are removed as bottoms and propylene oxide, propylene, propane, acetaldehyde and methyl formate are distilled overhead,

(e) directing the overhead from (d) to a C3 removal distillation zone where propylene and propane are distilled overhead and propylene oxide, acetaldehyde and methyl formate are removed as bottoms,

(t) passing said bottoms from said C3 removal zone to a distillation zone where acetaldehyde is distilled overhead and propylene oxide and methyl formate are removed at bottoms,

(g) passing the bottoms from (f) to an atmospheric extractive distillation zone using as extractive solvent a hydrocarbon solvent boiling above 67 C. and wherein methyl formate is removed overhead and said extractive solvent containing propylene oxide is removed as bottoms, and

(h) feeding the bottoms from (g) to a propylene oxide distillation rening zone from which purified propylene oxide is distilled overhead and recovered.

2. Process according to claim 1 wherein the overhead containing propylene and propane from said C3 removal zone in step (e) is fed to a propylene-propane distillation splitting zone to remove propane as bottoms and propylene as an overhead stream which is recycled to said reaction zone.

3. Process according to claim 1 wherein the overhead containing propylene and propane from said C3 removal distillation zone in step (e) is combined with uncondensed gases from said condensing zones and fed to said absorbing zone; feeding at least a portion of the bottoms from said absorbing zone to a desorbing zone from which solvent is removed as bottoms and combined with any solvent bottoms from said absorbing zone not fed to said desorbing zone and recycling this combined solvent bottoms stream to said reaction zone; passing the overhead stream containing propylene and propane from said desorbing zone to a propylene-propane distillation splitting zone to remove propane as bottoms and propylene as an overhead stream which is recycled to said reaction zone.

4. A process according to claim 1 wherein said solvent in said reaction zone comprises at least one fully esteriied polyacyl ester of a polyhydroxyalkane having from l-6 carbon atoms in each acyl moiety and from 2-6 carbon atoms in the alkylene moiety.

5. Process according to claim 4 wherein said polyacyl ester is ethylene glycol diacetate.

6. Process according to claim 4 ester is propylene glycol diacetate.

7. Process according to claim 4 wherein said solvent comprises a mixture of ethylene glycol diacetate and propylene glycol diacetate.

8. Process according to claim 1 wherein said oxidation occurs at temperatures within the range of from 50 C. to 300 C. and pressures within the range of from 0.5 to 350 atmospheres.

9. Process according to claim 8 wherein said oxidation occurs in the absence of added catalysts.

10. Process for the continuous production and recovery of propylene oxide which comprises the direct oxidation of propylene feedstocks with molecular oxygen in a reaction zone at a temperature of about 200 C. and a pressure of 50 atmospheres in a solvent selected from the group consisting of fully esteriiied polyacyl esters of polyhydroxyalkanes, polyhydroxycycloalkanes, polyglycols and mixtures wherein said polyacyl thereof wherein said esters contain from 1-6 carbon atoms in each acyl moiety and from 2-6 carbon atoms in each alkylene and cycloalkylene moiety, and recovering the thus-formed propylene oxide by:

(a) directing an effluent stream of the re-action mixture from said reaction zone to a irst distillation ashing zone operating at about 200 C. and 10 atmospheres pressure to remove major amounts of propylene oxide, acids and dissolved gases overhead to a first condensing zone and the bulk of said solvent as bottoms,

(b) passing the bottoms from (a) to a second distillation ashing zone also operating at about 200 C. and 2 atmospheres wherein most of the remaining propylene oxide and acids is taken overhead to a second condensing zone and said solvent is removed as bottoms,

(c) passing the bottoms from (b) to an absorbing Zone operating at about 70 C. at the top and 100 C. at the bottom and 8 atmospheres into which a stream of uncondensed gases from said first condensing zone is also fed, and propane, propylene and small amounts of propylene oxide are absorbed in said solvent, while (d) directing a side-stream of said solvent bottoms from (c) to a residue-removal distillation zone operating at temperatures of about C. at the top and 216 C. at the bottom and a pressure of 1 atmosphere where polymeric residue having a boiling point above that of said solvent is removed as bottoms and solvent is removed overhead and combined with solvent bottoms from said absorbing zone and recycled to said reaction zone,

(e) combining condensed liquid streams from said first and second condensing zones and feeding this combined stream to an acids-separation distillation zone operating at 40 C. at the top and 210 C. at the bottom and 10 atmospheres pressure to remove acids as bottoms and an overhead stream comprising carbon atoms in cycloalkylene moiety, the improvement which comprises the stabilization of a solvent removal from propylene oxide reaction mixtures by:

ceeding one,

(b) passing overhead to condensing zones,

(c) passing uncondensed gases from (b) and bottoms from (a) to an absorbing zone Where fixed gases, CO and CO2 are vented overhead and soluble components are absorbed in said solvent which is removed as bottoms, while gases from said ilashing zones (d) directing a side-stream of the bottoms in step (a) to a residue removal distillation zone to remove as bottoms those components boiling higher than said solvent which is taken overhead, and

(e) combining the overhead from step (d) with the bottoms from step (c) and recycling this combined stream to said reaction zone.

16. In the liquid phase continuous production and recovery of comprising at least one fully esteriied polyacyl ester of polyhydroxyalkanes having from 1-6 carbon atoms in each acyl moiety and from 2-6 carbon atoms in the alkylene moiety, the improvement which comprises the stabilization of and solvent removal from propylene oxide reaction mixtures by:

(a) conducting an effluent stream of reaction mixture from a reaction zone operating at about 200 C. and 50 atmospheres to a iirst distillation ashing zone operating at about 200 C. and 10 atmospheres wherein substantially all propylene, xed gases, CO2, about one-third of organic acids, at least one-half of the propylene oxide, and from 6-8% of solvent are removed overhead to a rst condensing zone and solvent is removed as bottoms. (b) passing said bottoms from step (a) to a second as bottoms, (c) passing said bottoms from step (b) to an absorbing zone operating at about C. at the top and 100 zone, while (d) directing a side-stream of said solvent bottoms from step (c) to covery. 17. Process according to claim 14 wherein said solvent comprises propylene glycol diacetate.

References Cited UNITED STATES PATENTS 3,024,170 3/ 1962 Othmer et al. 203-67 3,097,215 7/1963 Courter et al. 203-42 3,153,058 10/1964 Sharp et al. 260`348.5 3,165,539 1/1965 Lutz 203-42 3,207,677 9/1965 Colton 203`88 3,254,962 6/1966 Fox et al. 20342 NORMAN YUDKOFF, Prim-ary Examiner. WILBUR L. BASCOMB, JR., Examiner.

ggo UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,350,419 Dated October 31, 1967 Inventor(s) H. R. Nulll Et Al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 4 line 17, "erthritol" should be --erythritol- See spec page l0, line 6.

Column 4, line 58, "erthritol should be -erythritol- See spec page ll, line 24.

Column ll, line l, "cycloalkyenes" should be -cycloalkenes See spec page 29 line 23.

Column ll, lines 35-41, "(c) directing a side-stream of said effluent solvent in (b) through a polymeric residue having a boiling point above that of said solvent removal distillation zone where residue is removed as bottoms and solvent is distilled overhead and combined with the solvent bottoms from said absorbing zone and recycled to said reaction zone.", should be (c) directing a side-stream of said effluent solvent in (b) through a residue removal distillation zone where polymeric residue having a boiling point above that of said solvent is removed as bottoms and solvent is distilled overhead and combined with the solvent bottoms from said absorbing zone and recycled to said reaction zone..

See spec Claim l (c) SIGNED AND SEALED JUL 1 4 1970 EAL) Attest:

Edward M. Fletcher, Ir.

| l vmmm E. www, JR. nesting Officer Conmissione'r of Pat-ents 

1. PROCESS FOR THE CONTINUOUS PRODUCTION AND RECOVERY OF PROPYLENE OXIDE WHICH COMPRISES THE DIRECT OXIDATION OF PROPYLENE FEEDSTOCKS WITH MOLECULAR OXYGEN IN A SOLVENT SELECTED FROM THE GROUP CONSISTING OF FULLY ESTERIFIED POLYACYL ESTERS OF POLYHYDROXYALKANES, POLYHYDROXYCYCLOALKANES, POLYGLYCOLS AND MIXTURES THEROF, WHEREIN SAID ESTERS CONTAIN FROM 1 TO 18 CARBON ATOMS IN EACH ACYL MOIETY AND FROM 2 TO 18 CARBON ATOMS IN EACH ALKYLENE AND CYCLOALKYLENE MOIETY, AND RECOVERING FORMED PROPYLENE OXIDE BY: (A) DIRECTING AN EFFUENT STREAM OF THE REACTION MIXTURE FROM A REACTION ZONE THROUGH A PLURALITY OF SUCCESSIVE FLASHING DISTILLATION ZONES MAINTAINED AT ESSENTIALLY THE SAME TEMPERATURE AS THE OXIDATION REACTION, BUT EACH SUCCESSIVE FLASHING ZONE BEING MAINTAINED AT PRESSURES SUBSTANTIALLY LOWER THAN IN PRECEDING ONES AND IN SAID REACTION ZONE IN ORDER TO SEPARATE MOST OF THE LOW AND INTERMEDIATE BOILING PRODUCTS AS GAS PHASE FROM THE BULK OF THE SOLVENT WHICH IS REMOVED AS BOTTOMS FROM EACH FLASHING ZONE AND DIRECTED TO THE SUCCEEDING ONE, (B) PASSING SAID GAS PHASE TO CONDINSING ZONES, FROM WHENCE UNCONDENSED GASES ARE DIRECTED TO AN ABSORBING ZONE INTO WHICH EFFUENT SOLVENT FROM SAID FLASHING ZONES IS ALSO PASSED TO ABSORB UNCONDENSED PROPYLENE AND PROPYLENE OXIDE, (C) DIRECTING A SIDE-STREAM OF SAID EFFLUENT SOLVENT IN (B) THROUGH A POLYMERIC RESIDUE HAVING A BOILING POINT ABOVE THAT OF SAID SOLVENT REMOVAL DISTILLATION ZONE WHERE RESIDUE IS REMOVED AS BOTTOMS AND SOLVENT IS DISTILLED OVERHEAD AND COMBINED WITH THE SOLVENT BOTTOMS FROM SAID ABSORBING ZONE AND RECYCLED TO SAID REACTION ZONE, (D) PASSING A COMBINED STREM OF CONDENSED LIQUIDS FROM SAID CONDENSING ZONES INTO AN ACIDS-SEPARATION DISTILLATION ZONE WHERE ORGANIC ACIDS ARE REMOVED AS BOTTOMS AND PROPYLENE OXIDE, PROPYLENE, PROPANE, ACETALDEHYDE AND METHYL FORMATE ARE DISTILLED OVERHEAD, (E) DIRECTING THE OVERHEAD DROM (D) TO A C3 REMOVAL DISTILLATION ZONE WHERE PROPYLENE AND PROPANE ARE DISTILLED OVERHEAD AND PROPYLENE OXIDE, ACETALDEHYDE AND METHYL FORMATE ARE REMOVED AS BOTTOMS, (F) PASSING SAID BOTTOMS FROM SAID C3 REMOVAL ZONE TO A DISTILLATION ZONE WHERE ACETALDEHYDE IS DISTILLED OVERHEAD AND PROPYLENE OXIDE AND METHYL FORMATE ARE REMOVED AT BOTTOMS, (G) PASSING THE BOTTOMS FROM (F) TO AN ATMOSPHERIC EXTRACTIVE DISTILLATAION ZONE USING AS EXTRACTIVE SOLVENT A HYDROCARBON SOLVENT BOILING ABOVE 67*C. AND WHEREIN METHYL FORMATE IS REMOVED OVERHEAD AND SAID EXTRACTIVE SOLVENT CONTAINING PROPYLENE OXIDE IS REMOVED AS BOTTOMS, AND (H) FEEDING THE BOTTOMS FROM (G) TO A PROPYLENE OXIDE DISTILLATION REFINING ZONE FROM WHICH PURIFIED PROPYLENE OXIDE IS DISTILED OVERHEAD AND RECOVERED. 